Our attention was first brought to iron nucleotides by the finding of relatively large amounts, in stored human red cells, of a compound which proved to be a 1:1 complex of ferric iron with ATP. Small amounts of the FeATP were then found in red cells of blood freshly collected from man, rabbit, pig and rat. Subsequent work with recticulocytes from rabbit, pig and rat revealed no FeATP but large amounts of a compound which was characterized as a 1:1 complex of ferric iron with guanosine triphosphate. Reinvestigation of the mature cells of these animals and man disclosed that all of the small amount of GTP present was in the form of the iron derivative. Possible roles for these iron nucleotides in the metabolism of fresh and stored red cells are being explored. Work has continued on the metabolism of adenine and of inosine when these compounds are given IV to rabbits over a wide range of doses, and on the use of rabbit blood stored under various conditions as a model for investigations pertaining to the in vitro preservation of human red cells. A review on the pharmacology and metabolism of adenine is being prepared.